Heat oil in a skillet over medium heat. Add onions and garlic and lower heat. Cook until lightly browned, several minutes. Add carrots, beans, tomatoes and mushrooms and cook an additional 4-5 minutes, stirring occasionally. Turn off heat. Mash slightly in pan, until beans are half crushed.
Place skillet mixture in large bowl with remaining ingredients and mix thoroughly. If mixture is too moist, add more breadcrumbs. Form into 12-15 patties and cook over medium heat in oiled skillet, about 4 minutes on each side or until heated through and slightly crispy on the outside (patties can also be baked on a cookie sheet for 25 minutes at 180C/350F). Serve on a bun.