Preheat the oven to 425°F (218°C). Line a large baking sheet with a silicone baking mat or unbleached parchment paper.
Put the bread crumbs and sea salt in a gallon zip-top bag and shake to combine them. In a small bowl, whisk the egg. Set the bread crumbs and egg aside.
Lightly pat the chicken dry and cut it into 1-inch (2.5-cm) pieces. Transfer the chicken in the bowl with the egg and stir to combine, so that every piece of chicken is coated in egg.
Put the coated chicken pieces into the bag of bread crumbs. Close the bag and shake it to coat the chicken in the crumbs. Place the breaded chicken nuggets on the prepared baking sheet.
Spray the nuggets with the oil spray. Bake them for 20 minutes, until they are golden brown on top. Place the cooked nuggets on a wire rack to cool.
Chicken nuggets will last 3 days in the refrigerator. To freeze the cooked chicken nuggets, cool them completely and freeze them in a freezer-safe bag for up to 3 months. You can put the chicken nuggets into lunchboxes frozen and they will thaw by lunchtime.
Serve the nuggets with your kids’ favorite dipping sauce, such as ketchup, honey mustard, or ranch.