Heat oil in a large saute pan. Wilt spinach in the oil. Add in a touch of salt and pepper. Strain off excess liquid. Cool and chop the spinach.
Heat oil in a saute pan. Add in the onions. Saute until translucent.
Whisk eggs until they are completely scrambled. Add the cream, salt, and pepper. Mix well. Fold in spinach, herbs, onion, and goat cheese.
Spray a pan or crock big enough to hold all the egg mix. Bake until solid. There should be little to no movement when you shake the frittata. Time will vary depending on the size of the pan or crock. If you do individual frittatas it could take 15 to 20 minutes. A larger one could take 30 to 45 minutes.
The relish can be made ahead of time or while the frittata is cooking. Saute onion and garlic in olive oil until translucent. Add the sugar and melt it, stirring occasionally. Add in the white wine and reduce by 1/2. Then add in the tomatoes and stir in. Cook for just a couple minutes. You want them softened, but intact. Remove from the heat, season, and add in the herbs.
Serve the Frittata with the relish either on top or on the side.