Place kidney beans into a large container and cover with several inches of cool water; let stand 8 hours to overnight.

Drain and transfer beans to a stockpot. Add 1 1/2 quarts water (or as needed to cover) and bring to a boil. Add garlic, reduce the heat to low, and simmer until beans are tender, about 1 hour. Remove from the heat and stir in onion, bell pepper, oil, salt, and pepper.

Cook and stir rice in a large saucepan over low heat until toasted and fragrant, about 3 minutes. Add coconut milk, 3/4 cup water, and kidney beans; bring to a boil. Reduce the heat to low, cover, and cook until rice is tender, 30 to 40 minutes.