Cut the lettuce into thin strips (chiffonade). Slice the cucumber and radish into rounds or half-moons. Set aside.

Moisten the masa harina and form small, thick sopes. Set aside.

For the sauce, soak the guajillo chiles, then blend them with a little of the soaking water. Strain and set aside.

Blanch the oysters and set aside.

Cook and blend the tomatoes with oregano. Season to taste and set aside.

Cook the sopes on a griddle or skillet, then dip them in the chile sauce and fry until golden and crispy.

Fill each sope with refried beans, top with blanched oyster, crumbled Cotija cheese, and garnish with lettuce, cucumber, and radish slices. Serve with the tomato sauce.