Heat broth in saucepan and keep warm while preparing remaining ingredients.
Heat oil in large sauté pan Add sausage, sauté until browned, 10-12 minutes per side. Transfer sausage to paper towel lined plate. When cooled, slice into 1/2 inch rounds and set aside.
In the sausage pan sauté fennel and onion until they begin to soften and brown (about 5 minutes). Add garlic, pepper flakes and thyme and cook stirring constantly for 2 minutes. Transfer vegetables to a bowl.
Add orzo to the sauté pan, stirring to coat pasta with residual oil in the pan; cook 2 minutes.
Deglaze pan with wine. Add 1 1/2 warm broth to orzo; cook stirring constantly until broth is nearly absorbed; another 5 minutes. Add remaining 1 cup broth; cook and stir until liquid is fully absorbed.
Stir in sausage slices, vegetable mixture, then add parmesan, butter, parsley, lemon zest and chopped fennel fronds. Season with salt and pepper.