Preheat the oven to 350˚F (175˚C). Line 2–3 baking sheets with parchment paper or silicone baking mats.
Add 185 g all-purpose flour, 135 g old-fashioned rolled oats, 1 teaspoon baking soda, 1 teaspoon baking powder, ½ teaspoon fine sea salt, 2 teaspoons Tajín Clásico seasoning, and ¾ teaspoon ground cinnamon to a medium mixing bowl and whisk to combine. Set aside.
Add 50 g granulated sugar and zest of 1 lime to the bowl of a stand mixer fitted with the paddle attachment, or a large mixing bowl if using a hand mixer. Work the zest into the sugar with your fingertips until very fragrant and the sugar is slightly damp from the lime oil.
Add 150 g brown sugar and 170 g unsalted butter to the mixing bowl. Cream on medium-high speed until light and fluffy, about 2–3 minutes. Add 1 large egg and 1 teaspoon vanilla extract and beat until smooth.
Add the dry ingredients and mix on low until just combined. Add 75 g dried mango and 50 g white chocolate chips and mix on low just until distributed evenly.
Scoop the dough onto a baking sheet in about 2–3 tablespoon portions. Leave at least 2–3" (5–7.5 cm) of space between each cookie. To decorate, press a few pieces of dried mango and white chocolate chips or chunks on top of each cookie, and sprinkle on some Tajín.
Bake until spread and starting to turn golden around the edges, about 12–14 minutes. Leave to cool on the baking sheet for 5–10 minutes then transfer to a wire rack to cool completely.
