Stuffed Pepper Casserole (via the kitchn)

Ingredients

1 medium yellow onion
1 medium green bell pepper
1 medium red bell pepper
3 tablespoons olive oil, divided
1 pound lean ground beef
1 1/4 teaspoons kosher salt, divided
5 cloves garlic
1/4 teaspoon red pepper flakes
3 tablespoons tomato paste
1/2 teaspoon dried oregano
1 1/2 cups low-sodium chicken broth
1 (14.5-ounce) can diced fire-roasted tomatoes
2 teaspoons Worcestershire sauce
1 cup long grain white rice, preferably jasmine
1/4 teaspoon freshly ground black pepper
2 ounces low-moisture mozzarella cheese, shredded (about 1/2 cup)
2 ounces sharp cheddar cheese, shredded (about 1/2 cup)
4 large sprigs fresh parsley

Arrange a rack in the middle of the oven and heat the oven to 350°F.
Prepare the following, adding each to the same medium bowl as it is completed: Dice 1 medium yellow onion (about 2 cups). Trim and dice 1 medium green bell pepper and 1 medium red bell pepper (about 1 3/4 cups each).
Heat 1 tablespoon of the olive oil in a Dutch oven medium-high heat until shimmering. Add 1 pound lean ground beef, season with 1/2 teaspoon kosher salt, and cook, stirring occasionally and breaking up meat with a wooden spoon, until cooked through and browned, about 5 minutes. Transfer to a plate and drain off the fat in the pot if needed.
Return the pot to medium-high heat. Add the remaining 2 tablespoons olive oil and onion mixture. Cook, stirring occasionally, until the vegetables start to soften, about 5 minutes. Meanwhile, mince 5 garlic cloves.
Add the garlic and 1/4 teaspoon red pepper flakes and cook, stirring, until the garlic is fragrant and light golden-brown, about 1 minute. Add 3 tablespoons tomato paste and 1/2 teaspoon dried oregano and cook, stirring often, until tomato paste has darkened in color, 1 to 2 minutes.
Return the beef and any accumulated juices to the pot. Add 1 1/2 cups low-sodium chicken broth, 1 (14.5-ounce) can diced fire-roasted tomatoes and their juices, and 2 teaspoons Worcestershire sauce. Scrape up any browned bits from the bottom of the pan if needed. Add 1 cup long grain white rice, the remaining 3/4 teaspoon kosher salt, and 1/4 teaspoon black pepper, and stir to combine. Bring to a boil.
Cover and transfer the pot to the oven. Bake until the rice is tender and the liquid is absorbed, about 20 minutes. Meanwhile, grate 2 ounces low-moisture mozzarella cheese (about 1/2 cup) and 2 ounces sharp cheddar cheese (about 1/2 cup) on the large holes of a box grater. Pick the leaves from 4 large sprigs fresh parsley and finely chop until you have 2 tablespoons.
Remove the pot from the oven, uncover, and stir. Turn the oven to broil. Sprinkle the top evenly with the cheeses. Return the pot to the oven and broil uncovered until the cheese is melted, bubbly, and golden, 4 to 5 minutes. Let cool 10 minutes before sprinkling with the parsley and serving.