Start by making the corn tortillas. Combine masa, water, butter and salt. Mix until well combined and hydrated enough to feel like playdough.
Divide dough into desired number of tortillas and roll into balls. Place dough on parchment paper and use tortilla press or rolling pin to flatten into a tortilla shape. Cook in a hot cast iron skillet until done.
For the arugula mint pesto, start by toasting the nuts. Add the toasted nuts, arugula, Parmesan, and mint to a food processor. Blend until smooth. Drizzle in olive oil and 1 tablespoon of water while blending until it reaches a pourable consistency. Season the pesto with salt and pepper as desired and set aside.
For the flank steak, rub each quarter with salt, pepper, and arugula mint pesto to taste. Sear on grill until medium rare and set aside to rest.
For the grilled toppings, start by brushing the pineapple with olive oil. Season lightly with salt and grill until charred on all sides.
Cut lemon into 4-5 thick slices and lightly coat with olive oil. Grill lemons until charred on both sides and reserve.
Toss vegetables in olive oil, salt, and pepper to taste. Grill until desired doneness.
To assemble the tacos, add flank steak and grilled toppings to the corn tortillas as desired. Top with extra arugula mint pesto, and enjoy!