Nemco are GODS in food prep equipment. I bought an Easy Slicer with adjustable blade on Craig’s List for $75 delivered. I cannot imagine the sun even rising in the sky before this machine arrived in my life. We used to mangle our bell peppers on a straight blade mandolin every week. If the peppers were not precisely crisp, then they get mushy and don’t cut so well as fingers.
The Easy Slicer is multi-purpose, and has been used to cut tomatoes, onions, mushrooms, lemons . . . dice zucchini (had to cut into sticks first), and shave chocolate. If I am doing one or two pieces of something, my 10" chef knife will be quicker. But, when doing 5# of onions, the slicer zips through and gives a consistent slice width. See if you can find one used . . . they are over $200 new. I have not yet regretted the decision, and it would have paid for itself inside 6 months if I had bought it new. I was buying pre-sliced onions and throwing out 20%-30% usually. Now I pay a fraction per pound for whole onions, and get 100% usage out of a 25# case.
Get off the frozen diced peppers and get a slicer . . . you will not regret it. Even the lever action one Paul7979 showed will be good with several blade sizes for various application. Be gentle with the tomatoes, though, so you don’t mush them before slicing.