Step 1: Prepare your canning equipment by washing jars and lids in hot, soapy water and keeping them warm in your water bath canner.
Step 2: Peel the tomatoes by blanching them in boiling water for 60 seconds and then plunging them into an ice bath; the skins should slip off easily.
Step 3: Core and chop the peeled tomatoes, placing them in a large, heavy-bottomed stainless steel pot.
Step 4: Add the chopped onions, bell peppers, jalapeños, garlic, salt, sugar, cumin, and lemon juice to the pot.
Step 5: Bring the mixture to a boil over medium-high heat, stirring constantly to ensure the bottom doesn't burn.
Step 6: Reduce the heat and let the salsa simmer for 20-30 minutes until it reaches your desired thickness.
Step 7: Stir in the fresh cilantro during the last 5 minutes of simmering to preserve its bright flavor.
Step 8: Ladle the hot salsa into the warm jars, leaving 1/2 inch of headspace at the top.
Step 9: Remove air bubbles by sliding a non-metallic spatula around the inside of the jar and wipe the rims clean with a damp cloth.
Step 10: Place the lids and bands on the jars, tightening to fingertip-tight, and process in a boiling water bath for 15-20 minutes (adjust for altitude).
Step 11: Remove jars from the canner and let them cool undisturbed for 24 hours before checking the seals and storing in a cool, dark place.