In a medium bowl, combine canned tuna with mayonnaise, mustard, salt, and black pepper. Stir in diced jalapeños, chopped cilantro, diced red onion, and lemon juice until well combined.

For an ultra-smooth filling, pulse the mixture in a food processor until creamy, then fold in some jalapeños and onions by hand.

Preheat a grill pan or panini press over medium heat. Lightly grease it and toast slices of thin sourdough bread until golden brown.

Spread a layer of pesto on one slice of toasted bread.

Layer with creamy avocado and optional tomato slices. Add jalapeños if making a spicy version.

Spoon a generous portion of tuna filling onto the avocado layer.

Spread chipotle aioli on top (optional), then press another slice of bread to seal the sandwich. Cut in half and serve immediately.