Prepare the tuna. Drain the cans of tuna thoroughly through a fine mesh strainer set over a bowl. Line a small rimmed baking sheet or plate with parchment paper and set aside.
Mix the burgers. While the tuna is draining, in a large bowl combine the lemon zest and juice, 1 parsley, scallion, roasted red peppers, panko breadcrumbs, smoked paprika, egg, salt, and black pepper. Gently flake the drained tuna apart with your fingers and add to the bowl. Mix well until thoroughly combined.
Form the burgers. Divide the mixture into four even pieces. Gently roll each piece into a ball and then flatten into a patty. Place each patty on the prepared baking sheet.
Chill the burgers. Refrigerate the patties for at least 20 minutes and up to 1 hour. This will help them hold together while cooking.
Cook the tuna burgers. After the patties have chilled for at least 20 minutes, heat 2 tablespoons olive oil in a large skillet over a medium-high until the surface just begins to shimmer. Carefully add patties to the pan and sear, rotating the pan for even heat, for about 3 minutes, or until golden brown. Flip the patties and brown for 2 minutes more. Top patties with 4 ounces thinly sliced manchego cheese and cover the pan for 1 minute, or until cheese is melted and the bottom of the patty is nicely browned.
Finish and serve. Toast brioche burger buns until golden brown. Smear each side of the buns with aioli and/or bravas sauce, or any other toppings you prefer. Place patties on prepared buns and top with shredded lettuce.