Pizza Stuffed Mushroom Burgers

Ingredients

• 16 oz. (1 pound) bulk Italian sausage - plant-based or traditional
• 1/2 medium red onion, diced
• 1 bell pepper (any color), diced
• 3/4 cup sliced black olives
• 1/2 tsp. Italian seasoning
• 1/2 tsp. kosher salt
• 1/4 tsp. ground black pepper
• 4 portobello mushrooms
• ~1 Tbsp. extra-virgin olive oil
• Kosher salt and ground black pepper, to taste
• 3/4 cup marinara sauce
• 4 slices provolone cheese (or mozzarella)
• 4 hamburger buns of your choice
• Baby spinach leaves, for serving
• 1/4 cup prepared basil pesto
• 1/2 cup mayonnaise