In a large cast-iron skillet over medium-high heat, cook beef, breaking up into small pieces with a wooden spoon; season with salt and pepper. Add taco seasoning, tomato paste, and 2 Tbsp. water. Cook, stirring occasionally, until beef is browned and cooked through, about 5 minutes. Remove from heat.
Into another large skillet, pour oil to a depth of ½". Heat over medium-high heat until hot but not smoking. Fry tortilla strips, turning halfway through, until golden brown, about 2 minutes. Transfer to a paper towel-lined plate; immediately season with salt.
In a large bowl, season lettuce with a pinch of salt. Add tomatoes, beans, and beef mixture and toss to combine.
Top with cheese, pico de gallo, cilantro, and tortilla strips. Dollop with sour cream.
