ONIONS / Prepare BBQ medium high heat

Arrange onion rounds on a cookie sheet. Brush with olive oil; sprinkle with ? teaspoon coarse salt and fresh ground pepper.Transfer onion rounds (still intact) to grill rack; close cover. Cook until grill marks appear, about 4 minutes per side.Reduce heat or move onions to a cooler part of the grill. Close cover. Cook until onions are tender, about 10 minutes.Transfer to medium bowl. Toss with vinegar. Can be made up to 3 days ahead. Cover and chill

CHIPOTLE KETCHUP

Mix ketchup, chiles, adobe sauce and 2 tablespoons balsamic vinegar in a small bowl. Season with salt and more vinegari if desired. Can be made up to 3 days ahead. Cover and chill.

BURGERS

Shape beef into 6 ? thich patties. Sprinkle both sides with coarse kosher salt and fresh ground pepper.

Prepare BBQ medium high heat

Place burgers on the grill and close cover. Cook burger until bottoms start to brown and juices rise to surface, about 3 minutes.Turn burgers; cook to desired doneness, about 3 minutes longer for medium rare. Top with onions and cheese; close cover. Cook until cheese melts.

BUN

Place grilled muffin or bun bottoms on plates; spread with ketchup. Top with burgers; tomatoes (if desired), spinach and muffin or bun tops. Serve; passing the remaining ketchup