Heat 1 tablespoon of the oil in the skillet. Add the mixed mushrooms and cook over moderately high heat until any liquid has evaporated and the mushrooms start to brown, 5 minutes. Add the onion and remaining 1 tablespoon of oil; season with salt and pepper. Cover and cook over moderate heat, stirring, until the onion is softened, 5 minutes. Add the garlic, cover and cook over low heat, stirring a few times, until fragrant, 2 minutes. Add the wine and cook for 2 minutes. Add the tomatoes and simmer for 4 minutes.