1/2 teaspoon ground black pepper, plus more for seasoning
1 large bell pepper, cored, seeded, and cubed
1 large onion, cubed
For the Salsa:
3 dried guajillo chiles, stemmed and seeded
3 medium ripe tomatoes (about 1 1/2 pounds)
1 tablespoon olive oil
2 cloves garlic
1 1/4 teaspoon kosher salt
1 lime, juiced
1/2 cup cilantro leaves
6–8 skewers, soaked for at least 30 minutes before using if wooden
To marinate the skewers, separate the shrimp and beef into 2 bowls. Pour 1 tablespoon of oil in each bowl then divide the garlic, salt, oregano, and pepper between the two bowls and toss to combine. Cover and refrigerate for at least 1 hour or up to overnight.
In a large bowl, toss the vegetables with remaining tablespoon of oil and season with salt and pepper. Thread shrimp and steak onto the skewers separating the meat with the vegetables.
Heat a gas or charcoal grill to medium-high heat. Clean and oil the grates.
Meanwhile, prepare the salsa. Heat a dry skillet over medium heat and add the chiles. Toast them until they are fragrant and darkened in color, about 3-4 minutes, turning occasionally. Transfer to a heat proof bowl and cover with boiling water. Let soak while you prepare the tomatoes.
Cut tomatoes in half horizontally and scoop out the seeds. Toss tomatoes with the oil and place on the hot grill. Grill until skin is blackened and charred and tomatoes have slightly softened.
Let cool slightly, peel off skin and place in a blender with soaked chiles and remaining salsa ingredients. Blend until smooth. Taste and add more lime juice or salt if needed.
To cook kebabs, place on the hot grill and cook until shrimp are pink and firm and steak is cooked, about 4 minutes per side for medium-rare. Remove and serve immediately with salsa.