Cut tough stems off kale and discard. Stack leaves, roll tightly and cut crosswise into 3/4-inch strips. Transfer to a large bowl and cover with cold water; swirl to remove grit. Drain in a colander. Clean a second time if water in the bowl looks visibly dirty.

Heat oil in a saucepan over medium heat. Add onion and a pinch each of salt and pepper. Cook, stirring often, until golden brown around the edges, about 3 minutes. Add garlic and sage; cook and stir until fragrant, about 1 minute.

Stir in vegetable both, scraping up any browned bits from the bottom of the saucepan. Cover, reduce heat to low, and simmer, about 5 minutes. Increase heat to medium and add the kale. Season with salt and pepper and stir until just wilted, about 2 minutes. Cover and cook until tender but not soft, about 3 minutes.

Uncover saucepan; stir in beans and hot sauce. Stir until beans are heated through, 2 to 3 minutes. Season with salt and pepper.