1. Wipe mushrooms well with a damp cloth. Remove stems and chop stems only. Set aside for making filling in Step 3.
2. Saute mushroom caps in vegetable oil in a medium-size skillet 2 minutes, or just until heated through; place on a plate.
3. Saute chopped stems with grated onion just until soft in same pan; place in a small bowl; stir in liver pate and parsley.
4. Pile into mushroom caps. Garnish each with a quartered cherry tomato. Chill until serving time.