Preheat oven: 400°F (200°C). Line a baking sheet with parchment.
Mix filling: In a small bowl, stir together cream cheese and shredded cheddar. Set aside.
Make meatball mixture: In a large bowl, combine ground turkey, egg, breadcrumbs, diced jalapeños, green onion, garlic powder, onion powder, paprika, salt, and pepper. Mix until just combined.
Stuff the meatballs: Scoop about 2 tbsp meatball mixture, flatten slightly, add ~1 tsp cheese mixture in the center, and form into a ball. Repeat with remaining mixture.
Top with jalapeños: Place meatballs on the baking sheet and gently press a thin jalapeño slice on top of each one.
Bake: Roast for 18–20 minutes, or until cooked through (165°F internal temp).
Make the mash: While the meatballs cook, steam or boil cauliflower florets until fork-tender. Drain well. Add butter, Greek yogurt, garlic, ranch seasoning, salt + pepper, and blend until smooth and creamy.
Serve: Plate 3 meatballs per person with a generous scoop of ranch cauliflower mash.