Chinese long beans—18-inch green beans sold in Asian markets—stay crisp in stir-frys.
Whisk together soy sauce, rice vinegar, honey, sesame oil and red pepper flakes in bowl. Add tempeh and stir to coat. Marinate 30 minutes. Drain, reserving marinade. Whisk 1/4 cup water and cornstarch into marinade.
Heat 1 Tbs. vegetable oil in large nonstick skillet over medium-high heat. Add tempeh and stir-fry 4 minutes, or until golden. Transfer tempeh to plate with slotted spoon.
Add remaining 1 Tbs. vegetable oil to skillet. Add green beans and bell pepper, and stir-fry 6 minutes. Add mushrooms, and stir-fry 3 minutes. Add garlic and ginger, and stir-fry 30 seconds.
Add tempeh and marinade to skillet, and cook, 1 minute, stirring often, or until sauce thickens slightly. Sprinkle with green onions, and serve.