Soak dates in hot water to cover in a medium bowl for 10 minutes. Drain, reserving the soaking water.
Meanwhile, line an 8-inch-square baking pan with parchment paper, leaving extra hanging over 2 sides. Lightly coat with cooking spray.
Process oats in a food processor until finely ground. Add the drained dates, nut butter, cocoa powder and salt; process until very finely chopped. If the mixture seems dry, add a little of the reserved soaking water, 1 tablespoon at a time. Spread the mixture evenly and firmly into the prepared pan. Refrigerate until cold, about 1 hour. Remove from the pan by lifting the overhanging parchment. Cut into 16 squares.
To make ahead: Refrigerate for up to 4 days.
Tip: People with celiac disease or gluten sensitivity should use oats that are labeled “gluten-free,” as oats are often cross-contaminated with wheat and barley.
Serving size: 1 brownie
Per serving: 146 calories; 9 g fat(1 g sat); 3 g fiber; 14 g carbohydrates; 4 g protein; 13 mcg folate; 0 cholesterol; 7 g sugars; 0 g added sugars; 1 IU vitamin A; 0 mg vitamin C; 63 mg calcium; 1 mg iron; 73 mg sodium; 219 mg potassium