In a large bowl, combine the ground chicken, egg, Parmesan, breadcrumbs, milk, onion, jalapeño, garlic, salt, and pepper. Mix gently until just combined, being careful not to overwork the mixture.
Using a small cookie scoop or your hands, portion the mixture into about 20 meatballs, each approximately 1 inch in diameter.
Heat the olive oil in a large nonstick skillet over medium heat.*
Once the oil is hot, add the meatballs in a single layer. Cook, turning occasionally, until browned on all sides and the internal temperature reaches 165°F, about 10 to 12 minutes. Transfer the meatballs to a plate and tent loosely with foil to keep warm.
Reduce the heat to medium-low. Add the cranberry sauce to the same skillet, stirring and scraping up any browned bits from the bottom of the pan.
Cook for 2 to 3 minutes, or until the cranberry sauce is hot and loose enough to coat the meatballs. If the sauce is too thick, stir in water, 1 tablespoon at a time, until it reaches your desired consistency.
Return the meatballs to the skillet and gently toss until completely coated in the cranberry sauce.
Cook for another 1 to 2 minutes, just until heated through.
Garnish with thinly sliced jalapeño and parsley, if desired. Serve warm.