Tuna Melt Panini with Caramelized Onions and Swiss Cheese

By , Test Kitchen Director · Reviewed by AislePrompt Editorial · ·

A warm panini filled with creamy tuna salad, sweet caramelized onions, and melted Swiss cheese pressed to golden perfection. This american-inspired sandwiches & wraps ready in about 30 minutes pairs canned tuna in water, mayonnaise, Dijon mustard for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 550 calories and feeds 1, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

★ 4.3 (15 ratings) Prep: 20 min Cook: 10 min Serves 1 American cuisine 550 cal/serving
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Ingredients

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Instructions

  1. Step 1: Heat 1 tbsp unsalted butter in a skillet over medium-low heat. Add 1 small thinly sliced red onion and cook gently, stirring occasionally, for 15 minutes until onions are soft and golden brown and caramelized. Season with 1/8 tsp black pepper and a pinch of salt.
  2. Step 2: In a bowl, combine 5 oz drained canned tuna, 2 tbsp mayonnaise, 1 tsp Dijon mustard, and 1/4 tsp salt. Mix until creamy but still slightly chunky.
  3. Step 3: Preheat panini press or grill pan over medium heat.
  4. Step 4: Brush 2 slices sourdough bread lightly with 1 tsp olive oil on one side each. On the un-oiled sides, spread the tuna mixture evenly on one slice. Top with caramelized onions and then 2 slices (about 2 oz) Swiss cheese.
  5. Step 5: Close sandwich with the other slice of bread, oil side up. Place in the panini press and cook for 3-4 minutes until bread is golden brown and cheese is melted, or grill in a skillet pressing sandwich with a heavy pan, flipping halfway.
  6. Step 6: Remove from heat, let rest for 1 minute, then cut diagonally and serve hot.

Frequently asked questions

How long does Tuna Melt Panini with Caramelized Onions and Swiss Cheese take to make?

Total time is about 30 minutes (20 min prep + 10 min cook). Most home cooks find this fits comfortably into a weeknight; double the batch on Sunday for two dinners.

How do I store leftover Tuna Melt Panini with Caramelized Onions and Swiss Cheese?

Refrigerate in a covered airtight container for up to 3–4 days (FDA FoodKeeper guideline for cooked fish). Store any fresh salsa or citrus-based garnish in a separate container — it keeps for up to 2 days. Freeze cooked fish (without fresh garnishes) for up to 3 months; thaw overnight in the fridge and reheat gently at 275°F until just warmed through to preserve texture.

Can I substitute ingredients in Tuna Melt Panini with Caramelized Onions and Swiss Cheese?

Yes — most ingredients in this recipe have flexible swaps. For oil, use any neutral high-smoke-point oil (avocado, grapeseed, refined coconut). For aromatics, dried herbs at ⅓ the volume of fresh work in a pinch. The full ingredient list is shoppable on Instacart so you can see substitutes in real time.

How do I scale Tuna Melt Panini with Caramelized Onions and Swiss Cheese for a different number of people?

The recipe is written for 1 servings. Multiply each ingredient by (your serving target / 1). Cook time stays roughly the same up to 2x; for 3-4x batches, switch from a skillet to a sheet pan or stockpot so the food isn't crowded — overcrowding steams instead of browns.

What goes well with Tuna Melt Panini with Caramelized Onions and Swiss Cheese?

American sandwiches & wraps like this pair well with a simple grain (rice, couscous, or crusty bread), a quick salad with acid (lemon vinaigrette, pickled onions), and a pan sauce or yogurt-based dip. Tap "Plan a meal with the AI" to get specific side suggestions.

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