1. In a large bowl, toss coleslaw mix with jalapeno brine.
2. In a medium skillet, heat oil over medium-high heat. Add onion and cook until tender, about 4 minutes. Add chopped jalapenos and cook 1 minute more. Add beans and water and cook, stirring frequently and lightly mashing, until mixture has thickened, about 3 minutes.
3. Divide bean mixture among tortillas and top with coleslaw mix, tomatoes, cotija and cilantro. Serve with lime wedges if desired.