Combine marinade ingredients in an 8-inch baking dish. Set aside.
Score tempeh on both sides, making diagonal cuts 1/4-inch deep and 1/4 inch apart. Repeat in the opposite direction to form a diamond pattern. Scoring helps the tempeh to absorb the marinade.
Cut the tempeh into 6 portions then spread out in marinade dish and turn coating evenly. Cover dish and marinate for 2 to 6 hours while turning pieces frequently.
Heat olive oil then using a slotted spatula, lift tempeh from marinade place in skillet and brown for 1 to 2 minutes on each side over high heat. Remove to a serving dish and set aside.
Pour remaining marinade into the skillet and add pineapple with its juice and the green onions. Bring to a boil.
Combine cornstarch and water in a small cup or bowl and pour into boiling pineapple mixture a little at a time, stirring constantly, until thickened to desired consistency, about 1 minute. Pour over browned tempeh.
For Valentines Day or romantic dinner:
Using a cookie or canape cutter, cut 3 large hearts and 2 small hearts from the bell pepper, and dice about 1/4 cup of remaining red bell pepper.
Decorate plate with parsley and arrange the hearts attractively just before serving.