MIX sauce ingredients in a bowl.
STEAM tempeh on stovetop or in microwave. For stovetop: Place steamer basket in a saucepan and fill with water about 1-inch deep, or until the waterline is just below the steamer basket. Bring to a simmer, then add cubed tempeh to steamer basket. Cover and steam for 10 minutes. For microwave: Add cubed tempeh to a microwave-safe bowl with 2 tbsp of water. Cover and microwave for 2 ½ minutes. MARINATE tempeh in 2 tbsp of the sauce for at least 15 minutes.
HEAT avocado oil in a deep pan or wok. Add onion, garlic, and ginger and stir fry until onions turn translucent, 3-5 minutes.
ADD tempeh, bell pepper, zucchini, broccoli, and pineapple and stir fry another 5 minutes or until the veggies are tender.
GIVE the sauce a quick stir, then pour into the pan. Toss well to coat all the ingredients with sauce. Turn off the heat once the sauce thickens.
GARNISH with green onions and toasted sesame seeds. If desired, you can serve the pineapple tempeh with cauliflower rice or in lettuce cups.