Remove casings from sausage. Heat olive oil in a skillet over medium. Add sausage and cook, stirring to crumble. Meanwhile dice bell peppers. Add to sausage and cook for 2-3 minutes longer or until sausage is no longer pink. Drain excess fat and pour sausage into an 8x8 baking dish. Sprinkle with cheese.
Whisk eggs together with salt and pepper; pour over the sausage. Bake for 20-25 minutes or until eggs have fully cooked.
Meanwhile, chop fruit into smaller pieces and toss into a bowl with yogurt, vanilla, maple syrup, zest and juice of lemon, and walnuts; mix well. Refrigerate until ready to serve with casserole.