Fermented black soybeans, also called salted black beans, are sold in small plastic bags in the Asian section of many supermarkets. If you can’t find them, substitute 2 Tbs. prepared black bean sauce and decrease soy sauce to 1 Tbs.
Steam tempeh in steamer basket over boiling water 10 minutes. Whisk together soy sauce, black beans, garlic, ginger, sesame oil and 1/4 cup water. Toss tempeh with soy sauce mixture in bowl, and let stand 10 minutes.
Combine broth, cornstarch and vinegar in small bowl. Set aside.
Heat oil in skillet or wok over medium-high heat. Add asparagus, bell pepper and mushrooms, and stir-fry 3 minutes. Add tempeh mixture, and stir-fry 2 to 3 minutes more, or until vegetables are crispy. Pour in broth mixture, and cook 1 minute more, or until sauce is thickened. Serve over rice, if desired.