Peel and slice kohlrabi bulbs in half and use a melon-baller to carve out the center.
Place kohlrabi halves in a pot of boiling water and boil just until tender (20-30 min). Set aside on paper towel to dry.
In a separate pot, boil quinoa with 1 tbsp rosemary and vegetable broth. When the quinoa is done, set aside. Preheat oven to 400F.
Using 1 tsp olive oil, cook onions and carrots until onions are translucent and carrots are tender. Add garlic and cook for another minute. Add tomatoes and cook until the tomatoes are warm. Combine 1 cup quinoa with vegetable mixture and lemon juice. Add salt and pepper to taste.
Fill tender kohlrabi halves with quinoa mixture and place on a baking sheet. Bake at 400F for 20-30 minutes (until kohlrabi is almost soft, but still holds its shape).
While kohlrabi is baking, prepare the bechamel: melt 2 tbsp butter in a medium sauce pan; then add 2 tbsp flour; combine with a whisk. Then, add salt. Stir occasionally over low heat for 4-5 minutes. Slowly add 1 cup milk, stirring to combine. (Don't worry if it starts to look chunky, just keep stirring!). When milk is entirely added, place rosemary and lemon peel in saucepan with milk. After about two minutes, add lemon juice, stirring occasionally, until sauce is thickened to your liking. Remove rosemary & lemon peel.
Serve kohlrabi halves over bechamel and enjoy!