In zip-top plastic bag, or plastic container with a lid, mix together oil, adobo, garlic and pepper flakes. Add shrimp, tossing to combine; transfer to refrigerator. Chill shrimp at least 15 minutes, or up to 30 minutes.
Remove shrimp from marinade; reserve any remaining liquid. Alternately thread peppers, shrimp and lemons on skewers, so that each skewer starts and ends with peppers and contains 4 shrimp pieces. Using pastry brush, brush reserved marinade onto shrimp and vegetables.
Prepare grill to medium-high heat, or heat a heavy-bottomed grill pan over medium-high heat. Place shrimp on hot surface and cook until shrimp turn pink and opaque, flipping once, 3 – 5 minutes.
If your shrimp slip or spin around the skewer when you try to flip them on the grill, the result could be an unevenly-cooked crustacean and unnecessary frustration. Next time, make sure the shrimp stay put by using two skewers: Simply thread the shrimp with the first skewer and align second alongside to form two parallel lines. Then, grill with ease.