Brush the tortillas with oil and cut them in strips, about 1/2 inch wide and 2 inches long. Toast in the oven or toaster oven until just lightly toasted, which should take 4 to 5 minutes. Keep an eye on the strips—they can quickly go from perfectly toasted to burnt. Set them aside.
Heat about a tablespoon of oil in a soup pot on low flame. Sauté until the green garlic is translucent but not brown, stirring often. Add the vegetable stock and the tomatoes, along with the bay leaves, thyme and cracked peppercorns. Bring the pot to a simmer. Add the sorrel and spinach and cook and stir another minute.
Remove the thyme sprigs and the bay leaves. Stir in the lime zest and juice. Season to taste with salt.
Serve immediately, garnished with the tortilla strips and avocado, if desired.