Boil water in large pot with salt.
Add pasta and cook until al dente.
Drain pasta and rinse with cold water.
Let pasta cool completely in colander.
Dice all vegetables into uniform pieces.
Combine oil, vinegar, and lemon juice.
Add mustard, garlic, and oregano to dressing.
Whisk dressing until well combined.
Mix pasta with all chopped vegetables.
Pour dressing over pasta mixture slowly.
Toss everything together until evenly coated.
Refrigerate for at least 30 minutes.
Taste and adjust seasoning before serving.