Prepare barbecue (medium-high heat). Thread jalapeño and garlic clove onto metal skewer.
Brush jalapeño, garlic, fish, and red bell peppers with oil; sprinkle with salt and pepper.
Sprinkle fish with 1/2 teaspoon cumin and 1/2 teaspoon coriander. Grill fish, bell peppers,jalapeño, and garlic until vegetables are tender and charred and fish is just cooked through, about 4 minutes per side for fish and 8 minutes per side for vegetables. Grill lemon, cut side down, until charred, about 3 minutes.
Transfer fish to plate and tent with foil to keep warm.
Peel charred parts of skin from bell peppers and cut stem from jalapeño, and transfer to blender, discarding peel and stem.
Add garlic clove, remaining 1/4 cup oil, 1 1/2 teaspoons cumin, and 1 1/2 teaspoons coriander to blender. Process until coarse puree forms. Season sauce generously to taste with salt and pepper.
Place 1 fish fillet on each of 4 plates. Squeeze grilled lemon over. Spoon sauce over fish and serve.
One serving contains the following: Calories (kcal)445.46;%Calories from Fat
