Squeeze as much liquid as possible from thawed chard; chop and set aside.
Remove casings from sausages, crumble meat into a wide frying pan, and cook, uncovered, over medium-high heat until browned.
Add onion and garlic; cook, stirring, until onion is limp.
You may want to drain fat from pan at this point.
Stir chard into pan; cook, stirring, until all liquid has evaporated (about 1 minute).
Beat eggs until blended; pour over chard mixture.
Reduce heat to medium-low and cook, gently lifting cooked portion to allow uncooked portion to flow underneath, until eggs are softly set.
Transfer eggs to a warm serving dish.
Encircle with tomato wedges and serve with Parmesan cheese to sprinkle over individual servings.