Melt 2 tablespoons of the butter in a large skillet over medium heat with the olive oil. Add the onion and garlic; cook stirring often, until the onion is translucent, about 5 minutes.
Stir in the lima beans, stock, salt, pepper, and thyme. Bring to a simmer; cook, stirring occasionally, until the beans are tender, about 5 minutes.
Add the corn, bell pepper, cherry tomatoes, and vinegar. Simmer, stirring occasionally, until the liquid is mostly evaporated, about 5 minutes. Remove from the heat; stir in the remaining 1 tablespoon butter and the green onion just before serving.
