Sweet and Spicy Grilled Cheese Sandwiches - Ellie Krieger

Ingredients

• 2 teaspoons canola oil
• 1 large red onion, finely diced (about 2 cups)
• Salt and freshly ground black pepper to taste
• 3 ounces sharp cheddar cheese, thinly sliced
• 8 slices whole-wheat bread
• 3 ounces pepper Jack cheese, thinly sliced
• 1 large or 2 medium ripe beefsteak or hothouse tomatoes, sliced