Preheat the oven to 425°F. Combine the millet, 1¼ cup water, and a pinch of salt in a small saucepan and bring to a boil. Cover, reduce heat to low, and cook until all of the water is absorbed and the grains are tender, about 12 to 15 minutes.
Trim about 1 inch off the ends of the broccolini and discard. Add the broccolini to a baking sheet and toss with 2 tsp olive oil and a pinch of salt and pepper. Roast until crispy and browned in places, about 10 to 12 minutes.
Peel and dice the cucumber. Chop the romaine heart. Quarter the radishes. Roughly chop the mint leaves. Rinse the black-eyed peas and add them to a large bowl. Add the chopped vegetables and chopped mint to the large bowl.
Halve the lemon and cut half into wedges. In a small bowl, combine the juice from half the lemon, champagne vinegar, sumac, just 1 tbsp pomegranate molasses, 2 tbsp olive oil, and a pinch of salt and pepper. Whisk well. Add 2 tbsp of the sumac vinaigrette to the chopped vegetables and toss to combine.
Place a large nonstick skillet over medium heat and add the walnuts. Toast, shaking the pan frequently, until fragrant, about 3 to 4 minutes. Drizzle with the remaining pomegranate molasses and a pinch of salt and cook until sticky, about 1 minute more. Remove from the heat and toss with as much or as little cayenne pepper as you’d like.
Divide the chopped vegetables between large plates and top with the millet, roasted broccolini, pomegranate walnuts, and sumac vinaigrette. Serve with lemon wedges.