In a medium bowl, soak the bread with 2 tablespoons water (or 4 tablespoons for 4 servings); use your hands to break it up until it forms a paste. Stir in the ground beef, sriracha, scallion whites, half of the chopped garlic, salt (about 3/4 teaspoon kosher salt, or 1 1/2 teaspoons for 4 servings), and pepper.
Form the mixture into two 1-inch-tall loaves (or four loaves for 4 servings). Place them on one side of a baking sheet. On the empty side of the same sheet, toss the prepared carrots with a drizzle of oil, salt, and pepper. (If making 4 servings, you might need to spread the meatloaves across the whole sheet and use a second sheet for the carrots.) Bake for 20 minutes; you'll add the glaze later.