At least one hour before serving, place the scallops, lime juice, cilantro, jalapeno, red onion, and salt and pepper as desired in a medium bowl. Stir to combine ingredients. Cover and refrigerate for 1 hour or up to 12 hours.
On a large serving platter, place large lettuce leaves overlapping each other in a circle so the frilly edges extend just beyond the rim of the platter. Using a slotted spoon to leave juices behind, mound seviche in the center.
Place corn, chili powder, and 1 1/2 tablespoons of olive oil in bowl; mix together and season to taste with salt. Arrange corn in a ring around seviche so that the corn covers the bottom third of the lettuce leaves. Place tomatoes in an overlapping ring surrounding the corn and covering the middle third of lettuce leaves.
Distribute pressed garlic over the tomatoes, drizzle remaining oil on them, and season to taste with salt. Place the avocado slices and lime wedges on the top third of the lettuce leaves, around the tomatoes. Serve immediately.