Cook the quinoa: combine quinoa with the water and 1 teaspoon of salt in a medium saucepan over medium-high heat. Bring to a boil and simmer until all of the liquid is absorbed, about 10-15 minutes. Remove from the heat and set aside to cool.
IF ROASTING THE FENNEL: Preheat the oven to 400°F and line a baking sheet with parchment and set aside. IF GRILLING THE FENNEL: Preheat your grill to high.
Grill the fennel: brush the halved fennel with some olive oil and season with salt and pepper. Place onto the grill, cut side down. Grill until char marks are achieved on both sides and fennel feels a bit soft, about 4-5 minutes per side.
Remove the fennel from the grill and cut into a rough small dice. I do this by placing the flat side of the fennel down, cutting into lengthwise slices and then cutting those slices into smaller pieces.
Or roast the fennel: slice the halves of fennel and toss them in a bit of oil, salt, and pepper. Spread them out on the lined baking sheet and roast in the oven for about 15 minutes, or until soft and there are golden, caramelized edges.
Fluff the cooled quinoa with a fork and place into a large bowl. Add grilled and chopped fennel, radishes, cucumber, dill and green onions. Add dijon, lemon juice and the 3 tablespoons of olive oil on top. Season liberally with salt and pepper and mix until thoroughly combined. Garnished with the toasted nuts/seeds (if using) and reserved fennel fronds if you like.