Preheat the oven to 375°F. Bring a large pot of salted water to a boil.
Cook the rotini 1 minute less than package directions. Drain (do not rinse) and set aside.
In a 12-inch skillet over medium-high heat, heat olive oil and add ground beef. Cook, breaking apart, until browned (5–6 minutes). Transfer beef to a plate, leaving 1 tablespoon drippings in skillet.
Reduce heat to medium. Add diced onion to skillet and cook 3–4 minutes until softened. Add garlic and cook 30 seconds until fragrant.
Stir in frozen corn and 2 tablespoons ranch seasoning. Cook 1 minute, stirring constantly, until corn is warmed and seasoning is fragrant.
Sprinkle flour over the mixture and stir to coat. Cook 1 minute, stirring constantly. The mixture will look dry and pasty.
Slowly whisk in milk and chicken broth. Continue whisking until mixture comes to a gentle simmer and thickens enough to coat the back of a spoon (3–4 minutes).
Add softened cream cheese in chunks, whisking until smooth. Stir in 1 cup shredded cheddar until melted. Return beef to skillet and stir. Season with salt and pepper to taste.
Add cooked rotini to the skillet and stir until every piece is coated. The mixture will be slightly loose.
Transfer to a 9x13-inch baking dish. Top with remaining 1 cup cheddar and crumbled bacon.
Bake at 375°F for 15–18 minutes, until cheese is melted and bubbly and edges are golden. Let rest 5 minutes, then garnish with green onions before serving.