Rinse quinoa in a fine mesh sieve very well, for about 2 minutes under running water. Transfer to a medium saucepan and combine with two cups water and 1/2 teaspoon salt. Bring to a boil, then cover and reduce heat to low and simmer until liquid is absorbed, about 15 minutes. Uncover and fluff quinoa with a fork. To prepare ahead, refrigerate cooked quinoa overnight in a covered container.

In a large bowl, whisk together the lime zest, lime juice, olive oil, honey, 1/4 teaspoon salt, and pepper.

Add quinoa to dressing and toss until dressing is absorbed. Stir in black beans, grape tomatoes, and cilantro. Season to taste with additional salt and pepper if needed. Serve at room temperature or chilled.

Line two baking sheets with parchment. Combine butter, brown sugar, and salt in the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until the butter combines with the sugar but isn't perfectly smooth, 1 to 2 minutes. Add the flour and oats and mix on low speed, scraping the bowl as needed. Mix only until the dough has just about pulled together, about 3 minutes. Do not overmix.

On a lightly floured surface, roll the dough to about 1/4 inch thick. Cut the dough into squares or use a cookie cutter to cut out shapes, cutting them as close to one another as possible. Press dough scraps together, re-roll to 1/4 inch thick, and cut out additional cookies. If the dough becomes too sticky, refrigerate it briefly. Arrange cookies on the two prepared baking sheets and refrigerate until chilled, at least 20 minutes.

While dough is chilling, heat oven to 300 degrees. Place oven racks in the top and bottom thirds of the oven. Bake the cookies until golden on the bottom and edges and pale-to-golden on top, about 30 minutes to 1 hour. Swap the position and rotate the baking sheets after 15 minutes for even baking. Cool in pan for a couple of minutes, then transfer to a wire rack and allow to cool to room temperature.

Optional: In a small microwave-safe bowl, microwave the chocolate in 20 second bursts, stirring between each, until the chocolate is melted and smooth. Using a spoon or spatula, transfer the melted chocolate to a plastic bag, squeeze it into one corner of the bag, then snip off the very tip of the corner. Drizzle chocolate over the cooled cookies. Refrigerate until set, 15 to 20 minutes.