Cook grains following package directions. Transfer to a large bowl. Prepare rest of salad while you let grains cool completely.
Rinse fennel, greens, beet and apple.
Cut any long stalks and fronds of fennel. Quarter fennel and cut out core. Slice thinly.
Remove stems from greens. Stack leaves together, roll into a thick log, and slice thinly.
Peel and cut beet into ¼-inch cubes. Cut apple into ¼ cubes.
Peel and mince garlic.
If using, crumble cheese or cut into 1/4-inch cubes
In a small skillet over medium-low heat, add nuts or seeds. Cook until fragrant, 3-5 minutes. Transfer to a small bowl to cool.
Rinse and cut lemon in half. In a small bowl, squeeze juice. Discard any seeds.
Add vinegar, minced garlic and mustard to lemon juice. Whisk with a fork to combine. While whisking, slowly drizzle in oil. Season with salt and pepper.
When grains are cool, add fennel, greens, beet and apple. Drizzle with dressing and toss to combine. Sprinkle with the toasted nuts and cheese, if using.