Cactus pads, or nopales, have been consumed for generations. Studies suggest that nopales may control blood sugar levels in some people. I think they have a flavor similar to green beans. They are available at most Latin markets and come cleaned to make it much easier to prepare at home.
For the stuffing: In a medium saute pan over medium heat, add the olive oil, cactus, onions, garlic and salt and cook, stirring often, until the vegetables sweat, about 5 minutes. Continue to cook, stirring often, until the onions are fully cooked, 5 to 7 minutes longer; set aside.
For the chicken: Place about 2 tablespoons of the cactus stuffing on one side of each chicken breast. If you have remaining stuffing, reserve it for garnish. Top with the cheese. Using a brush, coat the edges of the chicken breasts with the egg and fold over the chicken to close.
Heat a saute pan over medium-high heat and add the canola oil. Season the chicken breasts with the salt and pepper. Carefully place each stuffed breast in the hot pan. Cook each side until seared and a nice crust forms, about 3 minutes. Transfer the chicken to a sheet pan and bake until the internal temperature is 165 degrees F, about 25 minutes.
For the sauce: Reduce the heat to low under the saute pan that was used for the chicken. Add the cumin, coriander and paprika and cook, stirring, until toasted, for a minute or two, taking care not to burn the spices—add a little oil to the pan if it looks dry. Add the lime zest and juice and cook, stirring, until the juice has reduced. Very carefully add the tequila; it may ignite, but not for too long. Stir in the chicken stock, salt and pepper; lower the heat and cook until reduced, about 10 minutes.
Place the chicken in a serving dish, cover with the sauce and garnish with any reserved cactus stuffing and chopped fresh parsley.