How to Make It
Heat a large cast-iron skillet over medium-high heat. Add 2 tablespoons oil to pan. Add tempeh; cook 4 minutes, turning to brown evenly. Drizzle soy sauce into pan. Immediately remove tempeh from pan; keep warm.
Increase heat to high. Add remaining 2 tablespoons oil to pan. Add onion and bell pepper. Cook 3 minutes, stirring occasionally. Add kale, salt, and pepper to pan; cook 1 minute, tossing to combine. Add vinegar to kale mixture; toss to coat. Divide mixture evenly among 4 plates; top evenly with tempeh.