In a heavy-bottomed large stockpot or dutch oven, brown the beef over medium-high heat, breaking it up with a wooden spatula. Sprinkle with salt.
When the meat is browned, add the diced onions and poblanos, stirring them in well. Cook 4-5 minutes, reducing the heat if necessary to soften the vegetables.
Add the garlic and tomatoes, stir well and continue to cook down for 4-5 minutes. Add the cumin, chili powder, Mexican oregano, and additional salt and pepper.
Add in the tomato paste and stir well to incorporate. Cook 1 min. Add in the beef stock. Stir well, add cilantro and place the lid on the stockpot. Heat to medium and cook 12-20 minutes, stirring twice during cooking.
Prepare the garnishes now.
For the tortilla strips: Cut the corn tortillas into thin ribbons. Heat the oil over medium-high heat. Fry one handful at a time in the oil until the strips are crispy and golden brown. Remove to a plate lined with paper towels to drain and salt well. Repeat with the remaining tortilla strips.
Remove the lid and stir well. Stir in the cornstarch slurry, whisking well. If the mixture is not boiling let the soup return to a boil, so that it may thicken with the slurry.
Finish with the juice of a lime and season to taste.
Serve in individual bowls topped with the fried tortilla strips, and any additional garnishes of your choosing.