Prepare all vegetables by washing and patting dry. Dice tomatoes into uniform 1/4-inch pieces, removing excess seeds if desired for less watery salsa.
Finely dice the red onion and sweet bell pepper into pieces slightly smaller than the tomatoes for balanced texture in every bite.
Mince garlic cloves and jalapeño peppers. For mild salsa, remove all seeds and membranes from jalapeños. For medium heat, keep half the seeds. For hot salsa, include all seeds and membranes.
Finely chop fresh cilantro, discarding thick stems but keeping tender ones for added flavor.
In a large mixing bowl, combine diced tomatoes, onion, bell pepper, garlic, jalapeños, and cilantro. Mix gently to distribute ingredients evenly.
Add fresh lime juice, salt, cumin (if using), and black pepper. Stir thoroughly to combine all seasonings.
Taste and adjust seasoning as needed - add more lime juice for acidity, salt for flavor enhancement, or jalapeños for additional heat.
Let salsa rest at room temperature for 10 minutes to allow flavors to meld, then serve immediately or refrigerate until ready to use.