Step 1

Heat an oiled grill pan over medium-high. Add scallions to hot pan and cook, flipping once, pressing down with a spatula occasionally, until grill marks appear and scallions are charred in spots, 1 to 2 minutes per side. (Alternatively, broil scallions in oven on a baking sheet until charred in spots, about 3 minutes.) Transfer to a cutting board and roughly chop; you should have a heaping ⅓ cup.

Step 2

Add beans, chives, mayonnaise, oil, lemon juice, and salt to a blender or food processor and blend until smooth, about 30 seconds. Add spinach and chopped scallions; blend, stopping to push contents down and scrape sides of bowl as needed, until smooth and creamy, about 2 minutes.