Cheapest/Easiest way to just draw a bunch of pixels right to the screen

Hey! I'm making a simple pixelly world map creator and I'd like to know what's the most efficient way to draw individual pixels. I need to maintain individual control over each pixel, as each directly corresponds to a 'cell' which will have map values such as height, habitability, temperature, etc.

I've tried two approaches.

The first was having a simple square quad prefab which I could then instantiate a bunch of and custom colour. This had the advantage that each pixel could store its own values.

I thought it'd be cheaper to simply have one large, screen-filling quad and change its texture directly, but surprisingly I found it to be more demanding. (Though it occurs to me now that maybe I could make the camera view really small so that each pixel corresponds to an actual texel.) Is there an extremely obvious approach I'm missing? Still pretty new to Unity. Thanks!

Anyway, this is an idea of the kind of view I want. (This is just a bunch of randomly generated map regions, each randomly coloured.)