Combine the lemon juice, chile pepper(s), garlic, paprika, pimentón, salt, and 1/4 cup of the cilantro leaves in a blender, and puree. With the motor running, slowly drizzle in the 1/3 cup olive oil to form an emulsion, and continue to blend for 1 minute, until the mixture is uniform. Transfer to a small serving bowl and stir in the remaining 1/4 cup cilantro. Set aside.

Heat 2 tablespoons of the olive oil in a 12-inch sauté pan over medium-high heat. Add the bell peppers, onion, a few generous pinches of salt, and a pinch of black pepper, and cook until the vegetables are lightly browned and soft, stirring occasionally, 5 to 6 minutes. Remove from the pan and set aside on a large plate.

Add the remaining 1 tablespoon olive oil to the sauté pan. Add the sausage, in batches if necessary, and cook until browned and blistered, 2 to 3 minutes per side. Transfer to the plate with the peppers and onion.

Arrange the toasted bread on a clean work surface. Place 2 sausage pieces on each bottom half of the bread. Drizzle with 1 to 2 tablespoons of the sauce. Divide the pepper-and-onion mixture among the 4 sandwiches, and drizzle a bit more of the sauce on top. Gently press the top halves of the bread over the filling, and serve immediately.