In a bowl, combine the ground beef, red onion, red bell pepper, sofrito, adobo, salt, black pepper, egg, and breadcrumbs. Mix until everything is well incorporated, then roll into 12 evenly sized meatballs and set aside.
Heat olive oil in a pan over medium heat and sear the meatballs until browned on all sides. Remove from the pan and set aside.
In the same pan, add the red onion, red bell pepper, green bell pepper, and sofrito. Sauté until the vegetables soften.
Pour in the tomato sauce, water, sazón, and salt, stirring to combine. Let the sauce simmer for about 5 minutes.
Return the meatballs to the pan, partially cover with a lid, and let simmer for 20 minutes, stirring occasionally, until the sauce thickens and the meatballs are fully cooked.
Serve warm and enjoy. Buen provecho!