Cut the ampalaya in half lengthwise. Scrape out the seeds and white pith, then slice thinly.
Rub with salt and let sit for 10 minutes. Rinse under cold water while gently squeezing, then drain well.
In a bowl, combine the ampalaya, onion, and tomatoes.
In a small bowl, mix the vinegar, garlic, sugar, salt, and pepper until the sugar dissolves. Taste and adjust.
Pour the dressing over the vegetables and toss gently.
Refrigerate for at least 30 minutes. Toss again before serving.
Notes
Ampalaya: Also called bitter melon or bitter gourd. Slice thinly for the best crunch. To lessen the bitterness, rub with salt, let sit for 10 minutes, then rinse and drain well.
Vinegar: Cane or coconut vinegar is best, but apple cider, rice, or red wine vinegar will also work.