1. In a small bowl, whisk together the vegetable broth, soy sauce, rice vinegar, ginger, and sugar.
2. In a large skillet, brown the tempeh in olive oil on all sides.
3. Add the bell pepper, snow peas, and scallions and heat just until vegetables are almost soft. Stir constantly.
4. Reduce heat and add the vegetable broth mixture. Whisk in cornstarch. Bring to a slow simmer and cook until thickened, stirring to prevent lumps.