Preheat oven to 350 °F (175 °C). Line baking sheets with parchment or lightly grease.

Make flax egg: combine ground flaxseed and water, set aside.

In one bowl, beat vegan butter, brown sugar, and granulated sugar until creamy.

Mix in flax egg and vanilla.

Add flour, oats, baking soda, cinnamon, and salt; mix until just combined.

Fold in chocolate chips. Cover bowl and refrigerate dough for at least 30 minutes.

Scoop ~1½ Tbsp dough balls, place on sheets, gently press down.

Bake 11–13 minutes until edges are set. Let cookies cool on sheet 5 minutes, then transfer to a rack.

Store at room temperature up to 3–4 days; dough and baked cookies freeze well—add 2 min to bake time if baking from frozen