Mix the refried beans and green chilis together in a large bowl. Spread the mixture out evenly in the bottom of a 9×9 inch baking dish.: The beans should feel warm and velvety against your spoon, and the faint aroma of the diced green chiles will hint at the flavor beneath. Use a rubber spatula to press and smooth the layer so it is compact and even, ensuring it will support the layers above. If the beans are too stiff, a tablespoon of warm water will make them glide easier, but avoid thinning them excessively. A common mistake is leaving the base lumpy which makes later spreads uneven, so take a few extra seconds to get a smooth, firm foundation.
In a medium bowl, mix the sour cream and taco seasoning together. Spread it out over the bean layer.: When you whisk the sour cream with taco seasoning , inhale the warm spices lifting from the bowl, and you'll notice the mixture takes on a uniform pale orange hue. Spoon dollops over the bean base and pull a flat spatula across to create a seamless layer. The reason this works is that the tang of the sour cream calms the spice and helps the avocado layer sit without sliding. Watch out for over thinning the sour cream, which can cause it to run into the beans and weaken the structure.
In a large bowl, mash the avocados. Stir in the cilantro, jalapeño, lime juice, and salt. Spread over the sour cream.: As you mash the avocados , you should see a silky, slightly chunky texture and smell a fresh, green note when you fold in the cilantro . The squeeze of lime brightens the fat in the avocado and prevents browning, while the jalapeño pepper adds quick sparkles of heat. Spread this layer gently so the guacamole sits atop the sour cream without mixing in. A common pitfall is over mashing to a puree, losing the pleasant textural contrast; keep some small pieces for interest.
Spread out the salsa, then romaine, cheese, olives, and green onions. Cover and chill until ready to serve.: The salsa should be distributed in an even, thin layer so its juices stay contained between the guacamole and lettuce. Next, scatter the shredded romaine lettuce to introduce cooling crunch, then pile on the shredded Mexican cheese for salty richness. Place the sliced black olives and then the green onions last to top with briny and sharp notes. Assemble with a light hand, preserving the visual bands of color. Avoid using watery salsa or over packing the lettuce which can make the dip soggy over time.
Cover and chill until ready to serve.: After assembly, the dish should feel cool to the touch and the layers firm. Chilling sets the structure and lets the flavors marry, creating a more integrated profile. I usually chill for at least thirty minutes, which firms the top layers and makes serving neat scoops easier. One mistake is chilling too long uncovered, which can dry the top; cover it to maintain moisture and freshness.