Blanch the Broccolini by putting it into a large saucepan of boiling water for 30 seconds. Remove Broccolini and plunge into a large bowl of ice water to stop the cooking process. Keep the water boiling. Strain and pat dry with paper towels. Add the fingerling potatoes to the water and boil until tender, about 10 minutes. Drain and run under cold water until cool. Pat dry. Use a knife to slice potatoes in half lengthwise. Set aside.
For the pesto, in a food processor add Broccolini, basil, Parmesan, salt, pepper, garlic, and olive oil. Pulse until all ingredients are blended together. Set aside.
Cut the onion into ½-inch slices. Heat a large sauté pan over medium-high and add oil to the pan. Add sliced onions and season with salt to taste. Sauté and stir occasionally with a wooden spoon until the onions begin to brown, about 8-10 minutes. Set aside.
In a large mixing bowl, add cooked fingerling potatoes, caramelized onions, peppers, corn, bacon, and half of the pesto. Toss to combine well and adjust seasoning with salt and pepper to taste.
Pile the salad on a serving platter and top with the remaining pesto and grated Manchego cheese. Serve immediately.