In a small bowl, combine the roasted piquillo peppers with 1/4 cup of the olive oil and set aside.
Mix together the ground meat, garlic and 2 tablespoons of the olive oil, and season with a pinch each of salt and black pepper. Form the mixture into eight 2-ounce patties.
Preheat a grill to high heat. Grill the patties until their internal temperature reaches 160 degrees, about 5-6 minutes on each side.
Brush the hamburger buns with olive oil and toast on the grill for 1 minute. Spread 1 tablespoon of aioli or mayonnaise onto the bottom half of each toasted bun followed by a burger patty.
Top with the marinated peppers and serve.