Peel the onion and garlic, finely chop and mix with mayonnaise. Season with salt and pepper. Wash the pork, dry it and cut it into 5x5 cm pieces. Put it in a bowl, pour the prepared mayonnaise marinade, mix thoroughly and leave for 40 minutes.
Remove the pork from the marinade, wipe with napkins. String on 4 skewers and grill for 20-25 minutes. Serve with ketchup.