Bring egg whites and lemon juice to room temperature.
Grind pepitas until fine using a food processor. Pulse and be careful not to over process as they will form a paste. Mine did have some pieces slightly larger than a sifter allows to pass. I still add them as long as they're not larger than 1/8 of a seed (realize you will be chewing them in a soft cookie).
Sift together the pepitas, cocoa powder, and powdered sugar.
In a mixing bowl with the whisk attachment, whip the egg whites and lemon juice until they are light and fluffy. Slowly add the granulated sugar. Continue to whip until stiff and peaks form.
Fold in the cocoa, pepita, and powdered sugar mixture. Fold until it falls from the spatula in one long piece.
Line baking sheets with parchment paper or silicone baking sheets.
Place batter in a piping bag (or zip-loc with corner cut off).
Pipe 1 1/2" circles on the parchment paper.
Leave out at room temperature for 45 minutes to allow a film to form across the tops.
Preheat oven to 400°F. Place the macarons in the oven and immediately turn the temperature to 300°F. Bake for 16-18 minutes, careful not to brown the tops.
Allow them to cool completely prior to piping ganache on top.