Heat a large skillet or sauté pan over medium-high heat and add the olive oil.
Add the chopped bell pepper and sauté 2 minutes, then add the broccoli florets and sauté another 3–4 minutes until partially softened; remove the vegetables from the skillet and set aside.
In the same skillet, add the whole chicken breasts, minced garlic, dried quinoa, 3 1/2 cups chicken broth, 1/2 teaspoon salt, 1/2 teaspoon crushed red pepper, and 1/4 teaspoon black pepper; stir to combine and bring to a simmer.
Lower the heat once simmering and cook until the chicken is cooked through, the broth is mostly absorbed, and the quinoa spirals have separated, about 18–20 minutes; add up to another 1/2 cup broth if the pan becomes too dry.
Remove the chicken to a cutting board, chop or slice it, then return it to the skillet.
Toss in the sautéed vegetables, pecan pieces, dried cranberries, and chopped scallions; stir to combine and taste, adjusting salt and pepper as needed.
Serve warm.