Bring a large pot of water to boil and cook pasta according to package instructions.
Gently wipe mushrooms to remove any dirt.
Slice each mushroom into about 4 pieces.
Add to a pan with the broccoli florets, add about 2 tbsp of oil and saute for about 5-7 minutes. Afterwards, drain off any extra liquid that was released from the mushrooms.
Mince the garlic and add to a large pot with the olive oil and cook until the garlic starts to brown.
Stir in the flour and whisk to get rid of any clumps.
Slowly stir in the non-dairy milk and continue to whisk.
Add the lemon juice and lemon zest if using.
Reduce heat to low and let simmer until the sauce has thickened. If the sauce doesn't thicken to your desired consistency after 10 minutes, whisk in an additional tbsp of flour.
Add the salt and pepper and stir.
For an ultra creamy sauce, transfer to a blender or use an immersion blender and process until completely smooth. I prefer blending the sauce because it infuses the garlic flavor into every bite and makes it incredibly creamy and silky.
Add the mushrooms, broccoli and sauce to the cooked pasta. Stir to incorporate.
Top with additional salt, pepper, or red pepper flakes if desired and enjoy!