Bring a large pot of heavily salted water to a boil. Add macaroni and cook according to package directions. Add broccoli for the last 5 minutes of boiling and let cook until broccoli is fork tender. Drain and return to pot.
Meanwhile, in a medium saucepan, make a roux or paste by whisking the margarine and flour over medium heat for 3 to 5 minutes. Add nondairy milk, yeast, tomato paste, salt, and garlic powder to the saucepan and bring to a boil, whisking frequently. Reduce heat to low and let simmer until the sauce thickens. Adjust seasoning to taste and stir in lemon juice and agave. Toss the noodles and broccoli with the sauce and serve immediately.