Make the marinade: Whisk all ingredients together in a large bowl.
Marinate steak: Place steak into the marinade mixture; toss to coat the steak in the marinade. Cover bowl and place in refrigerator. Let steak marinade for 30 minutes or up to 1 day.
Prep the ingredients per the instructions above.
Make the guacamole: Mash the avocado with a fork until it is smooth. Stir in the cilantro, garlic, and sour cream. Season with salt and pepper to taste. Refrigerate until ready to serve.
Remove the steak from the marinade. Mix the steak and shrimp together with 1/4 of the parsley, cilantro, garlic, and olive oil. Season well with salt and pepper.
Heat a skillet on medium heat. Add the steak and shrimp mixture to the skillet. Saute until steak is nicely browned and shrimp is cooked through, then set aside. Cook the steak to your desired temperature using a thermometer (see below). Set the steak aside to rest for 5 minutes before cutting it up into bite-sized pieces. Chop the shrimp.
Make the sauce: Place the remaining parsley, cilantro, garlic, and oil in a blender. Add the juice from the orange and pulse until blended well. Add more oil if needed for a smoother consistency. Season with salt and pepper to taste.
Lightly warm the tortilla shells on both sides in the skillet over medium heat.
Mix the ingredients for the mocktail until very well combined. Serve over ice if desired.
Serve: Layer the tortilla shells with steak and shrimp; spoon the sauce over top. Garnish with tomato and jalapeño if using. Enjoy with chips, guacamole, and mocktail.