1) Preheat a grill to medium-high. In a small bowl, combine cumin, garlic powder, thyme, salt, and pepper. Rub the spice blend over all of the steak pieces along with one tablespoon of the oil. Let rest at room temperature, about 15 minutes.
2) Meanwhile, in a large pot, add the remaining two tablespoons of oil and heat over medium heat. Add the onions and saute until tender, about four minutes. Stir in the mushrooms and garlic and saute until mushrooms are tender, adding extra oil if needed. Pour in the broth, jalapenos and crushed tomatoes. Bring to a boil then reduce heat and simmer while beef cooks.
3) On a hot grill sear steak until golden brown on both sides, about five minutes per side. Remove from grill to a cutting board and let rest 10 minutes. Cut beef into strips and stir into soup, along with spinach. Season soup, to taste. Transfer to serving bowls and top with a dollop of sour cream and tortilla chips.