Combine the beef with the onion, both kinds of cheese, breadcrumbs, taco seasoning, cilantro, the whole egg and the bell pepper in a bowl. Use parchment paper to line a pair of baking sheets.
Arrange the wonton skins on a dry work surface and add a heaped teaspoon of filling in the center of each one. Scrunch the tops of the wontons up so they look like half-open moneybags. Alternatively you can close them, sealing the edges, to make triangle shapes of another wonton shape.
Arrange the finished wontons on the baking sheets, cover with plastic wrap and chill for 20 minutes. Preheat the oven to 500 degrees F (260 degrees C) and bake the beef wontons for 7 minutes or until the wonton wrapper is golden brown and the filling is cooked. Serve hot.