Baked Tilapia Sandwiches

Ingredients (9)

• + 4 (4 ounce) tilapia fillets add to pantry
• + 2 tablespoons olive oil, divided, or as needed add to pantry
• + ½ teaspoon Cajun seasoning, or to taste add to pantry
• + 1 pinch salt and ground black pepper to taste add to pantry
• ✓ 1 pinch salt and ground black pepper to taste
• + 2 medium onions, thinly sliced add to pantry
• + 1 (14.5 ounce) can diced tomatoes, drained add to pantry
• ✓ 2 tablespoons capers
• + 4 submarine sandwich rolls, split add to pantry