In large nonstick ovenproof skillet, heat oil over medium-high heat. Add onion and garlic; cook until lightly softened, about 3 minutes. Add potatoes; cook for 2 to 3 minutes.

In small bowl, beat eggs with salt and pepper; stir in ham and three-quarters of the cheese. Add to skillet; reduce heat to medium and cook until bottom is brown and crusty, about 5 minutes, occasionally lifting edges so uncooked eggs can flow underneath. (If skillet handle is not ovenproof, wrap in foil.)

Sprinkle half of remaining cheese over frittata; top with tomatoes and remainder of cheese. Broil until eggs are set and cheese is melted, 1 to 2 minutes. Cut into wedges to serve. Garnish with parsley.

Tip: If you don't have cooked potatoes, scrub raw potatoes, pierce well and microwave at High until almost cooked, 6 to 8 minutes. Cool slightly, then dice (leave skin on for added fibre).

Note: Microwave recipes tested in a 700-watt microwave oven. Power level terminology in microwave ovens varies; check your owner's manual and use whichever word or number gives you the same percentages as in the recipe (High is always 100%). If your oven differs, cooking times may vary.