Prepare all vegetables by washing, peeling, and chopping them into bite-sized pieces.
Layer the onions, carrots, and celery at the bottom of the crock pot.
Add the potatoes, green beans, zucchini, corn, and peas on top.
Pour in the diced tomatoes and vegetable broth.
Add minced garlic, dried basil, oregano, bay leaves, salt, and pepper. Stir to combine.
Cover and cook on Low for 6-8 hours or on High for 3-4 hours, until the vegetables are tender.
In the last 30 minutes of cooking, add fresh spinach or kale, if using.
Remove bay leaves before serving. Adjust seasoning if needed.
Serve hot, garnished with fresh herbs or grated Parmesan cheese.