Place a large pot over medium heat and add the ground beef. Cook, breaking it up with a spoon, until browned and no longer pink, about 6 minutes. Drain excess fat if needed.
Add the diced onion and minced garlic to the pot. Cook for 2 minutes until the onion starts to soften.
Stir in the zucchini, green beans, and red bell pepper. Cook for 3 minutes, stirring occasionally.
Pour in the diced tomatoes with their juice and the beef broth. Add the oregano, salt, and black pepper.
Bring the mixture to a simmer. Cook for 10 to 12 minutes until the green beans are tender but still bright.
Taste and adjust salt or pepper if needed, then remove from heat.