Heat 2 tbsp of oil in a wide, covered skillet or Dutch oven over medium heat, and add onion.
Cook, stirring, until tender and translucent, 5-8 minutes. Add the garlic and cook, stirring, for another minute until fragrant.
Stir in green beans, squash and remaining oil. Stir together for a few minutes, then add the tomatoes and 1/2 cup water. Bring to a simmer, add salt and pepper.
Cover and simmer for 30 minutes until the beans are tender and the mixture is stew-like. Add the herbs, and simmer for another 5-10 minutes.
Add lemon juice if desired. Taste, and adjust seasonings as needed.
Serve hot or at room temperature.