Cook spaghetti according to package instructions; drain and set aside.
In a large skillet, heat olive oil over medium heat.
Add ground beef to the skillet and cook until browned.
Drain excess fat from the skillet.
Stir in taco seasoning and diced tomatoes; simmer for 5 minutes.
Combine cooked spaghetti with the beef mixture; mix well.
Remove from heat and stir in half of the cheese until melted.
Transfer to a serving dish and top with remaining cheese.
Drizzle sour cream over the top and add diced tomatoes.
Garnish with chopped green onions and jalapeños if desired.