Warm the avocado oil in a large skillet over medium heat until it shimmers. Add the chopped onion and thawed corn, stirring occasionally. Sauté for several minutes, or until the onion becomes translucent and the corn starts to develop a light golden hue.
Incorporate the chopped red bell pepper, thawed lima beans, and drained diced tomatoes with green chilies. Season generously with salt and freshly ground black pepper. Allow the mixture to simmer for about 5 minutes, stirring occasionally, until most of the excess moisture has evaporated and the flavors have melded together.
Once cooked, transfer the succotash to a serving dish and garnish with freshly chopped basil. Serve hot as a vibrant side dish, or chill and enjoy it cold straight from the fridge.