Preheat the Oven Preheat oven to 375°F. Line a 13x9-inch baking pan with foil, taking care to not create holes in the foil. Coat foil with nonstick cooking spray.
Blend Ingredients In a blender combine eggs, half-and-half, ½ tsp. salt, and ¼ tsp. black pepper; cover and blend until combined.
Add Spinach Add spinach; cover and blend until just chopped. Pour mixture into prepared pan.
Bake in the Oven Bake until eggs are just set, 12 to 15 minutes. Remove from oven. Cool eggs in pan 5 minutes.
Cool on a Wire Rack Using foil, lift egg mixture from pan from pan and cool completely on a wire rack.
Fill the Focaccia Cut eggs into six portions. Split focaccia pieces in half horizontally. Spread cut sides with pesto and fill with egg portions, cheese, and ham, if using.
Wrap Sandwiches Cut sandwiches in half. Wrap sandwiches in parchment or plastic wrap, then wrap in foil. Chill up to 5 days or freeze up to 1 month.
Reheat in Microwave To reheat, remove foil and plastic wrap (if used). Wrap sandwich halves in parchment or waxed paper. Microwave on high until heated through, 1 ½ to 2 ½ minutes, turning every 45 seconds.
