Ingredients:2 teaspoons canola oil 1 large red onion, finely diced Salt Freshly ground black pepper 3 ounces sharp Cheddar, thinly sliced, divided 8 slices whole-wheat bread 3 ounces pepper Jack cheese, thinly sliced, divided 1 or 2 large tomatoes, sliced Cooking spray Directions:Heat oil in a nonstick skillet over medium-high heat. Lower heat to medium. Add onions and saute, stirring, until edges are browned, about 10 to 12 minutes. Season with salt and freshly ground black pepper, to taste.Place 3/4-ounce Cheddar on 1 slice bread. Spread 1 tablespoon caramelized onions on top of cheese and top with 3/4-ounce pepper Jack. Top with 1 large or 2 medium slices tomato and other slice of bread. Repeat with 3 other sandwiches.Spray a nonstick skillet or griddle with cooking spray and heat until hot. Place sandwich on griddle and weigh down with a heavy skillet or plate. Lower heat to medium-low and grill until underside is a deep brown but not burnt and cheese is partially melted, about 5 to 6 minutes. Flip sandwich and grill other side, an additional 4 to 5 minutes. Slice in half and serve hot.