Step 1

Have grill pre-greased and preheated to medium-high.

Step 2

Place fish in a non-reactive bowl. Add 3 cups of chilled water to fish and rinse gently. Drain water.

Step 3

Add onions to remaining chilled water and let soak.

Step 4

Meanwhile, place aji, garlic, and pinch of salt in a mortar and pestle. Grind to make a paste.

Step 5

Combine fish, lime and lemon juices, aji and garlic paste, salt, pepper, and cilantro. Let marinate for 10 minutes.

Step 6

Brush corn and sweet potato slices with oil and place on grill. Cook about 10 minutes.

Step 7

When ready to serve, divide fish ceviche among 4 lettuce cups and top with onion slices. Serve with grilled corn and sweet potato slices and garnish with Japanese seaweed, if desired.