Step 1

Purée chile, garlic, peach, sugar, and ¼ tsp. salt in a blender until smooth. Transfer purée to a small saucepan and cook over medium heat, whisking often, until starting to bubble around edges, about 4 minutes.

Step 2

Dissolve cornstarch in 1 tsp. water in a small bowl. Whisk cornstarch slurry into purée and simmer, whisking constantly, 1 minute. Stir in vinegar and let sauce cool.

Step 3

Prepare a grill for medium-high heat. Brush scallops lightly with oil; season with salt and pepper. Grill until charred and cooked through, about 3 minutes per side.

Step 4

Taste sauce and add more sugar, salt, or vinegar if needed. Spoon sauce onto a platter and arrange scallops on top. Scatter cilantro over and serve with lime wedges if using.