For the fish: Toss the mahi-mahi with the chili powder, cumin, lime zest and juice, 2 tablespoons vegetable oil, 1/2 teaspoon salt and some pepper in a large bowl. Let marinate at room temperature for 15 minutes while you prepare the slaw.
For the slaw: Crumble the ramen noodles into a large bowl. Add the cabbage, chayote, scallions, edamame, mango and radishes and toss to combine. Whisk the lime juice and honey together in a small bowl with 1 teaspoon salt and some pepper. Whisk in the vegetable oil and pour the dressing over the slaw. Toss well.
To cook the fish, heat a large nonstick skillet over medium-high heat. Add the remaining 2 tablespoons oil, then add the fish and cook, tossing once or twice, until browned and just cooked through, 3 to 4 minutes. Serve the fish hot in the tortillas, topped with the slaw, avocado and cilantro. Serve any additional slaw on the side.