Set oven to 350 degrees. Lightly grease a 9x5-inch loaf pan. In a skillet melt butter over medium heat, add in mushrooms, onion, red bell pepper, garlic and thyme; sauté for about 6 minutes, then transfer to a large bowl. Add in all remaining ingredients; using clean hands mix thoroughly. Place mixture into the prepared loaf pan, then place them onto a baking sheet to catch any spills. Bake for 50-60 minutes. Using 2 forks remove the meatloaf from the pan. Let rest 5-7 minutes before slicing.