Preheat the oven to 400° and line a baking sheet with parchment paper.
Bake in the preheated oven for 25 to 40 minutes or until they’re easily pierced by a fork, stirring the carrots halfway through the cook time.
Add the onion, 1 Tbsp. olive oil and the other 1/2 tsp. salt to the baking sheet for the last 5 minutes of cooking.
Squeeze the bag lightly to mix the ingredients, then remove excess air, seal, and freeze.
Thaw.
Pour the contents of the freezer bag into a large pot. Add two cups of water and bring the mixture to a boil over high heat.
Add lemon juice and pepper before serving.