For the Grilled Vegetable Relish

Prepare a grill with a medium-hot wood fire.

Shuck corn and remove silk. Peel onion and slice it in 1/2-inch rings. Do not separate rings. Brush canola oil onto the corn, onion, bell peppers, and Serrano pepper and place them on a clean grill rack over the medium-hot fire and close lid.

Grill corn until it gets char marks and becomes tender, about 10 minutes. Grill onions until they caramelize on both sides and become tender, about 10 minutes. Grill bell peppers and Serrano pepper until skin chars and turns mostly black, about 10 minutes. Turn all of the vegetables over halfway through cooking. Remove vegetables from grill. Place corn and onion slices on a plate to cool. Place peppers in a bowl and cover it with plastic wrap to steam.

Once the grilled vegetables are cool enough to handle, cut corn kernels off of the cob and place them in a mixing bowl. Cut onion rings into 1/2-inch dice and add them to corn. Wipe charred pepper skins away with a towel and discard. Pull peppers apart and discard seeds. Cut peppers into 1/4-inch dice and add to bowl. Cut tomato into 1/4-inch dice and mix with grilled vegetables. Add basil, vinegar, lemon juice and olive oil. Season with salt and pepper and mix thoroughly. Tightly covered, the relish can be refrigerated for up to 24 hours but should be brought back to room temperature before serving. Heat the relish if putting it into quesadillas.