If using wooden skewers, soak them in water for 20 minutes to prevent burning.
Whisk together the olive oil, garlic, lime juice, cumin, salt, and pepper.
Toss the shrimp, fish, scallops, bell pepper, and onion in the marinade.
Thread the seafood and vegetables onto the skewers, alternating pieces.
Preheat a grill or grill pan to medium-high heat.
Grill the skewers 3–4 minutes per side, until the seafood is opaque and lightly charred.
Serve hot, with extra lime wedges on the side.