Set oven to 350 degrees. Spray a 9x5-inch loaf pan with cooking spray.
Mince the mushrooms, onion and bell pepper. In a skillet over medium heat add olive oil in mushrooms, onion, red bell pepper, garlic (minced) and thyme; saute 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 pan, then place on a baking sheet to catch any spills.
Bake for 50-60 minutes. Let rest 5-7 minutes before slicing.
Bring a large pot of salted water to a boil.
Add potatoes and cook until tender, 20 to 30 minutes.
With an electric mixer on low, blend potatoes, slowly adding milk. Use more or less to achieve desired texture.
Add butter and maple syrup, to taste. Blend until smooth. Serve warm.