Heat the oil in a large pot over medium heat; cook and stir the onion and garlic in the hot oil until tender, about 5 minutes. Stir in the pork and cook until completely browned, 5 to 7 minutes. Stir the shrimp into the mixture; season with salt and pepper. Continue cooking until the shrimp turn pink, about 5 minutes. Add the tomato to the pot, cover, and let cook 5 minutes. Stir the zucchini, okra, green beans, eggplant, and bitter melon into the mixture; cover, and cook until the vegetables are all soft to the touch, about 10 minutes more. Serve hot.