Place the potatoes and butterbeans in a pot and cover with water. Bring to a boil and season the water with salt and pepper; reduce the heat to simmer. Cook until just tender, about 30 minutes. Drain well and set aside.
Heat the oil in a large skillet over medium-high heat. Add the onions and cook until soft and translucent, 3 to 5 minutes. Add the corn and squash and cook, stirring, until crisp-tender, about 5 minutes. Stir in the reserved butterbeans and potatoes. Cook, stirring, until heated through. Add the tomatoes, stirring to combine. Taste and adjust for seasoning with salt and pepper. Serve immediately.
Recipe courtesy of Virginia Willis