Place a beef in a 5 quart slow cooker. Coat a 12 inch nonstick skillet with cooking spray. Add onions, mushrooms, and garlic. Saute over medium high heat 5 minutes, stirring occasionally.
Place half of beans in a slow cooker. Place remaining beans in a blender. Add 1/2 cup of broth to blender and puree. Add mixture to slow cooker. Add remaining broth, tomatoes, oregano, dried thyme, salt and pepper to slow cooker.
Cover and cook on high setting of slow cooker for 6 to 7 hours. Garnish with fresh thyme if desired.