Add tomatoes (with juices), potatoes, carrots, celery, onion, garlic, bay leaf, basil, oregano, salt, pepper, and broth to a 6-quart slow cooker. Stir to combine.
Cover and cook on low for 6 to 8 hours or high for 3 to 4 hours, until the potatoes and carrots are tender.
About 30 minutes before the end of cooking, remove the bay leaf. Stir in the green beans and corn. Cover and cook until heated through.
Stir in the lemon juice just before serving to brighten the flavor.
Serve garnished with fresh thyme.
Notes
Substitute 3 cups frozen mixed vegetables for the green beans and corn if needed.
If using dried thyme instead of fresh, add ½ teaspoon along with the other dried herbs in Step 1.