In a small bowl, stir together 1 cup tomatoes, ¼ cup onion, the lime juice and ¼ teaspoon each salt and pepper. Set aside until ready to serve.
In a large pot over medium-high, heat the oil until shimmering. Add the remaining onion, garlic and ¼ teaspoon salt; cook, stirring occasionally, until beginning to brown, 3 to 4 minutes. Add the chipotle chili, adobo sauce and tomato paste; cook, stirring often, until the pastes begin to brown and stick to the pot, 1 to 2 minutes. Add the ground beef and oregano. Cook, breaking the meat into bits, until beginning to brown, 2 to 3 minutes.
Add 6 cups water and bring to a simmer. Add the pasta and 2½ teaspoons salt. Cook, stirring often, until al dente, 6 to 8 minutes. Add the remaining tomatoes and cook, stirring, until heated through, about 1 minute.
Off heat, stir in the heavy cream or evaporated milk, then taste and season with salt and pepper. Serve topped with a spoonful of the reserved salsa.
