Heat oven to 400° F.
Combine chard and cannellini beans in a large casserole, baking dish, or ovenproof skillet. Evenly distribute in a single layer -- or as close as you can get to a single layer. It will look like a lot of chard, but it will considerably cook down. Season with a few pinches of salt and pepper.
In a small bowl, whisk together lemon juice and zest, Dijon mustard, smoked Spanish paprika, and olive oil. Add to chard and cannellini beans and toss well with hands to evenly coat. Nestle the pieces of sausage on top of the chard and beans.
Roast for about 20 to 25 minutes, or until the chard is tender with crispy edges and the sausage is no longer pink. For extra security, you can toss about halfway through the cooking time to ensure even cooking.
Taste and add more salt, pepper, or lemon juice if needed. Top with grated parmesan or pecorino. Serve warm.